Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output and a flow of exhaust gases. The exhaust gases can include a complex mixture of air pollutants produced as byproducts of the combustion process. For example, an engine can produce NOx, particulate matter, and hydrocarbons. Due to increased attention on the environment, the amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine size of e and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes exhaust gas recirculation (EGR). EGR is the recirculation of a portion of the exhaust gas produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture when ignited, produces a lower combustion temperature and a corresponding reduced amount of NOx.
An exemplary EGR system is disclosed in U.S. Patent Application Publication No. US 2012/0222659 A1 to Kulkarni et al. that published on Sep. 6, 2012 (“the '659 publication”). The '659 publication. discloses a four-stroke engine having a plurality of donor cylinders and a plurality of non-donor cylinders. Exhaust gases from the non-donor cylinders are directed to a first exhaust manifold, which routes the exhaust gases through a turbine and to the atmosphere. Exhaust gases from the donor cylinders are directed to a second exhaust manifold, which routes the exhaust gases through an exhaust gas recirculation (EGR) system and into an intake passage for both the donor and non-donor cylinders. The EGR system includes an EGR cooler to cool the exhaust gases before the exhaust gases return to the intake passage. The donor and non-donor cylinders are positioned in two banks of cylinders, with some donor cylinders arranged in between non-donor cylinders along each of the two banks of cylinders. In addition, two or more of the donor cylinders may be positioned immediately adjacent one another at a middle point along one of the two banks of cylinders, in order to reduce engine noise and vibration and to reduce a size of the second exhaust manifold, which routes exhaust gas from the donor cylinders to the intake passage of the engine.
Although the system of the '659 publication may help lower engine emissions by re-circulating the exhaust to the intake passage of the engine, the system may still be less than optimal. Specifically, the system of the '659 publication may be applicable to four-stroke engines. Two-stroke engines, which do not have discrete intake and exhaust strokes, may experience problems with pumping the exhaust from the donor cylinders back into the intake passage of the engine. Additionally arranging the donor cylinders at locations in between the non-donor cylinders along the bank of cylinders may increase the size of the exhaust manifold associated with the donor cylinders and cause problems with packaging other components associated with the EGR system within the engine system.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.